This invention relates generally to sample handling systems for automatic and semiautomatic fluid analyzing systems and is concerned particularly with the provision of a system utilizing pneumatics and hydraulics to effect aliquot sample withdrawal and movement, with an isolation chamber provided to function as a buffer between the pneumatics and hydraulics for preventing surges, and as well, to provide a microcomputer as a control for operation of said system in conjunction with the optical analysis of the successive sample aliquots in the system which includes a flow cell.
Automatic and/or semi automatically operated testing apparatus require the taking of aliquot portions of a liquid sample to be tested, transferring these aliquots to a testing station, holding each aliquot at the testing station for the duration of the test and disposing of the tested aliquot from the testing station to a waste receiving location.
Successful operation of the testing apparatus demands careful control of the aliquot volume and its movement through the system. Pneumatic means such as vacuum and/or air pressure is utilized alone or in conjunction with the use of hydraulics can be employed to draw and to move the aliquot.
One problem encountered in the use of sample handling systems involving both pneumatics and hydraulics is occasioned by the generation of turbulence in the liquid causally related at least in part by the abrupt changes in pressure. Another involves the danger of carryover from one body of liquid occasioned by the relative relationship of the pneumatic and hydraulic systems, and their possible overlap. Turbulence sufficient to draw bubbles or to cause bubbles to be generated, produces erroneous results since the bubbles may be trapped in the test chamber of the testing apparatus, interfering with passage of the light beam.
Accordingly, it is desired to provide means to serve as a buffer between the pneumatic and hydraulic systems so that pressure changes occasioned in moving the liquid bodies can be applied through such means rather than directly to the conduits through which the liquid bodies travel, whereby smooth flow is obtained throughout the system and surges eliminated.
Another problem encountered may be attributable to the operation of the system at a slow rate, an often suggested and adopted solution for avoidance of turbulence in flowing liquid systems. Here the flow rate elected may be too slow, forming an optically interferent dead zone interior of the flow cell at the testing station in the general scheme of the system concerned.
Accordingly, the invention further provides a flow cell construction having a path arranged to improve the rate of flow through the flow cell.